Titanium alloys are in increasingly widespread use as material for the production of implants. The benefits of this material for use as prostheses include important properties such as a high mechanical load-bearing capacity, a high chemical stability and, not least, excellent biocompatibility. With regard to the material properties aspect, titanium alloys are the material of choice for many different types of implants, including bone plates, pins, artificial knee and hip joints as well intervertebral disk prostheses.
The prior art has disclosed various processes for producing the implants. The choice of a suitable process depends not only on the type of implant to be produced but also on the titanium alloy used in each instance. For shaping purposes, there are two main processes used for titanium alloys, namely forging, on the one hand, and investment casting, on the other hand. In principle, titanium alloys are forging alloys (Peters/Leyens: Titan and Titanlegierungen [Titanium and titanium alloys], Wiley-VCH-Verlag, 2002). However, investment casting has the advantage of allowing even complex shapes to be produced easily near net shape, whereas these complex shapes cannot be achieved by forging or can only be achieved by joining a plurality of components. However, the investment casting of titanium alloys generally causes problems on account of the high melting point and the high reactivity of titanium; an additional problem is the low density of the alloys. Only a few groups of titanium alloys are suitable for investment casting. These include in particular what are known as α-titanium alloys and some α/β-titanium alloys. From the latter group, in particular alloys comprising vanadium and aluminum, such as TiAl6V4, have become important for the production of implants. Implants, such as joint prostheses or dental implants, can be produced successfully from this alloy by investment casting.
However, there are certain concerns as to the long-term compatibility of the alloying elements which are typically used for α/β-titanium alloys, such as TiAl6V4. Moreover, the modulus of elasticity of these alloys is well above that of natural bone material, which can lead to pathological changes to the bone.